Monolithic metallic liner for fiberglass gun tubes

ABSTRACT

A tubular device suitable for use as gun barrels and the like and being capable of withstanding sudden high pressures normally encountered in ordnance use, the device having a nonstructural metallic inner liner of noncircular configuration overwrapped by fiberglass windings acting in a structural capacity, and a resilient elastomeric material disposed between the liners at substantially uniform spaced intervals.

United States Patent [72] Inventor Merrill Eig pp y. J.

[2]] Appl. No. 831,876

[22] Filed June 10, 1969 [45] Patented Mar. 23, 1971 I [73] Assignee TheUnited States of America as represented by the Secretary of the Army[54] MONOLITHIC METALLIC LINER FOR FIBERGLASS GUN TUBES 10 Claims, 5Drawing Figs.

[52] US. Cl 42/76, 89/16 [51] Int. Cl F4lc 21/02, F41d 17/06, F41d 17/08[50] Field of Search ..42/76, 76.1;

[56] References Cited UNITED STATES PATENTS 2,845,741 8/1958 D 42/76(.1)2,847,786 8/1958 Hartley et a1. 42/76(.1) 3,118,243 1/1964 Manshel42/76(.1) 3,228,298 1/1966 Grandy et al. 42/76(. 1) 351,758 6/1970 Slade42/76 Primary ExaminerBenjamin A. Borchelt Assistant Examiner-C. T.Jordan Att0rneys-Harry M. Saragovitz, Edward J. Kelly, Herbert Berl andS. Dubroff ABSTRACT: A tubular device suitable for use as gun barrelsand the like and being capable of withstanding sudden high pressuresnormally encountered in ordnance use, the device having a nonstructuralmetallic inner liner of noncircular configuration overwrapped byfiberglass windings acting in a structural capacity, and a resilientelastomeric material disposed between the liners at substantiallyuniform spaced intervals.

MONOLITHIC METALLIC LINER FOR FIBERGLASS GUN TUBES STATEMENT OFGOVERNMENT INTEREST The invention described herein may be manufactured,used and licensed by or for the Government for governmental purposeswithout the payment to me of any royalties thereon.

BACKGROUND OF THE INVENTION This invention relates to tubes or cylindersuseful as gun barrels and the like and more particularly concernscomposite tubes having a monolithic, nonporous, nonstructural, metallicinner liner surrounded by a nonmetallic, stnictural overwrap linerwherein good strain compatibility is effected between the liners whenthe tube or cylinder is subjected to sudden high pressures.

The desirability of improving gun barrels has long been recognized amongthe military, not only from the standpoint of enhanced logistics butalso troop combat efficiency. The military have long sought to achievegun barrels which are inexpensive to manufacture, light in weight, andyet erosion resistant and long lasting. The long felt need for a gunbarrel characterized by these properties is evidenced by the efforts ofprior patentees whose inventions for various and sundry reasons fellshort of filling the existing hiatus in the art. Illustrative prior artgun barrels are disclosed in the following patents, among others: U.S.Pats. Nos. 2,249,899 issued Jul. 22, 1941; 2,845,741 issued Aug. 5,1958; 2,847,786 issued Aug. 19, 1958; 2,935,913 issued May 10, 1950; and3,118,243 issued Jan. 21, 1964. For the most part these patents suggesta composite gun barrel construction wherein a metal core or liner isjacketed by plastic or resinous glass fibers. The function of the outerjacket material is dictated by considerations of lightness and strengthwhile the selection of the core or liner material is dictated byconsiderations of resistance to wear and erosion. While the underlyingrationale in the construction of the prior art launcher barrels appearssound, other considerations of a controlling nature either have goneunnoticed or have presented difficult problems for which solutions werefound wanting.

A primary consideration in the construction of composite gun barrels isstrain compatibility of the materials of construction. High rate ofloading conditions of short duration normally encountered in gun barrelusage make for an even more difficult problem because of the necessarymultiple considerations of the coefficients of expansion and thermalconductivity.

Another consideration closely related to strain compatibility is theobtention of more elastic means in the liner material. Where, as in theprior art gun barrels, a jacket of relatively elastic material having anelastic limit approaching 3 percent surrounds an inner liner ofrelatively inelastic material having an elastic limit approachingrpercent, it is obvious that the latter value is controlling.Accordingly, the use of a low elastic limit material in the inner linerlimits the full utilization of the fiberglass potential and results in aless efficient composite structure.

Accordingly, it is a principal object of the present invention toprovide a gun barrel of composite construction which is unattended bythe aforementioned disadvantages of the prior art.

Another object of the invention is to provide a lightweight gun barrelof composite construction characterized by freedom from defectsattributable to strain incompatibility arising from firing conditionsnormally encountered in usage.

The exact nature of the invention as well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification relating to the attached drawings wherein:

FIG. 1 illustrates a sectional view of an embodiment of my inventivetubular device as represented by a gun barrel showing the outernonmetallic liner, inner metallic liner, and elastomeric materialbetween the liners.

FIG. 2-5 illustrate modifications of the inner liner configuration.

Referring to the drawings and more particularly to FIG. 1 thereof, thereis shown a gun barrel having a nonmetallic outerwrap liner l0, suitablyof fiberglass windings, and a metallic, expandable inner liner 12 ofcorrugated or sine wave configuration. Any formable metallic materialwhich is capable of providing the required degree of erosion resistancemay be used for the expansible inner liner. Stainless steel worksadmirably, and when so used, I have found that a thickness of about0.010 to 0.020 inch is structurally satisfactory in obtaining largeelastic strains, i.e., greater than about one-half percent. The ratio ofouter liner to inner liner thickness is no particular importance sinceas a result of the high pressures prevailing in gun tubes upon firingtherethrough, the outer fiberglass is designed to be the structuralmember. The role of the liner is to resist erosion of the barrel andthis liner does not significantly contribute to the strength of theoverall system. Ordinarily, the ratio of fiberglass to metallic linerthickness is of the order of about 20 or 30 to 1.

Disposed between the inner liner 12 and outer liner 10 is a hightemperature elastomeric backup material 14, which aids in preventingcrushing of the inner liner and yet permits relative movement betweenthe inner liner and itself. The elastomeric material may be of hightemperature silicone, flexible epoxy or epoxy-novolac, a hard resin ofhigh elongation, or a high temperature polyurethane.

In order to more-fully appreciate the invention, it must be rememberedthat a basic problem in the successful cooperation between fiberglassand metallic components is that of strain incompatibility due todifferent expansion characteristics of these materials. Thisincompatibility is induced by one or a combination of the following:

a. internal pressurization b. thermal expansion c. thennal contractionIf one considers as a representative case the condition which existswhen a thin monolithic metallic liner contacts the inner wall of afiberglass tube, the resultant composite tube being heated rapidly to ahigh temperature, it will be realized that because of the difference inthermal conductivities, among other properties of the materials, themetallic liner will expand at a faster rate than the fiberglass to causebuckling of the restrained inner liner. Thus, to effect compatibilitybetween the liners, the geometry of the monolithic liner must be alteredsuch that the desired strain is a combination of material and geometricexpansion. The capability of the inner liner to be successfullysubjected to large strains, i.e., greater than about percent, beyondwhich point stainless steel and most other metals become substantiallyinelastic, is accomplished by means of flexing and extending thecorrugations as shown in FIG. 1 in the circumferential direction similarto movement of an accordion. In Table I below, results are presented forthe corrugated or sine wave inner liner. It can be seen that bothspecimens resisted strains greater than xzpercent. Specimen No. 1 wassubjected to a second cycle of 2,000 p.s.i., which yielded a strain ofonly 0.42 percent. The specimen was discarded as having served itspurpose but was still very elastic in nature. The elastomeric materialused was a high temperature polyurethane.

TABLE I.TEST RESULTS FOR CORRUGATED STAINLESS STEEL LINER PercentSpecimen strain Number Cycle Number Pressure (p.s.l.): l

l Hydrodynamic testing device used. 2 Strain guage Wire broke.

Referring again to FIG. 1, if a high pressure is generated within thebarrel, as upon the firing of a projectile therethrough, the erosionresistant corrugated inner liner 12 will be caused to expand against theelastomeric material 14 and fiberglass l0, portions of both the innerand elastomeric 'material being structurally restrained by the outerfiberglass liner.

The modification of FIG. 2 employs a square wave inner liner 22 whichcontains elastomeric material 24. If the square wave liner S2 isperiodically altered at a specified uniform spacing as at 52, all asshown in FIG. 5, such that its amplitude is higher than its adjacentwave, and the liner is then twisted at a desired angle relative to thelongitudinal axis of the barrel, (depending on the desired angle ofrifling) rifling may be obtained. The elastomeric material is shown at54.

The modification of FIG. 3 shows a modified square wave configuration,the inner liner 32 containing the elastomeric material 34.

In the modification of FIG. 4, the inner liner 42 is Z-shaped, theelastomeric material being shown at 44.

Tests conducted on the square wave configuration, modified square waveor gear tooth configuration, and the rifling and Z-shaped inner linersindicated that these modifications could be successfully substituted forthe corrugated inner liner configuration.

When over-winding the inner metallic liner with fiberglass, buckling ofthe former does not occur since;

(1) it is backed-up and supported by a mandrel, and

(2) the expansion characteristics of the inner liner will movably adjustin response to motion of the fiberglass. The mandrel need have nospecial configuration but should be of such as material to resist thehigh temperature experienced during the cure cycle, and will preferablybe cylindrical, upon which mandrel the inner liner may be rolled. Theelastomeric material will be coated or painted on the inner liner whileflat, the task being relatively simple, the configuration of the innerliner being considerably exaggerated in each of the drawings.

At this point, the outer surfaces of the inner liner may be coated witha thin layer of epoxy-novolac resin and the entire resultant assemblyoverwrapped in accordance with the following procedure:

Means are provided for rotating the mandrel about its longitudinal axiswhile drawing fiberglass strands from a spool riding on a reciprocatingcarriage which moves from one end of the mandrel to the other. Where thestrands are not preimpregnated, means may be provided for coating suchstrands with resin as they are drawn from the spool to the mandrel.Subsequent windings should comprise alternate groups or layers ofhelical and circumferential windings. Preferably, three-layers ofhelical windings at an angle of 209? relative to the mandrel axis followthe initial layer of circumferential windings. While both types ofwindings provide circumferential strength, the helical windingscontribute to strength in the longitudinal direction. For example, inthe construction of an 81mm. mortar, it is contemplated that the baseplug, preferably metallic, adapted to seat in a base plate and housingthe firing pin will comprise a ball or knob-shaped projection coaxialwith and attached to a closure or end cap, the latter having an outerdiameter substantially the same as that of the gun barrel to which thebase plug is attached. It is further contemplated that the base plugwill have a flange projecting from the end gap and forming a coaxial,hollow cylinder of reduced outer diameter, the inner diameter of thecylinder being equal to the inner diameter of the gun barrel. Byproviding the attachment end of the gun barrel with an undercut whichwill mate with the cylindrical flange of the base plug, proper alignmentand seating may be effected and attachment of the gun barrel to the baseplug will be facilitated. Accordingly, circumferential windings may beapplied over the aforementioned helical windings until the thickness ofthe gun barrel is built up to that of the base plug flange. Thereafter,another 3 layers of helical windings may be applied followed bysufficient layers of circumferential windings to build up to thepredetermined gun barrel outer diameter. The wound mandrel can then berotated in an oven to effect curing and upon completion of the curingoperation, finish sizing may be effected by cutting off barrel ends toarrive at the final barrel length and by machining the barrel to arriveat the final outer diameter. The mandrel can then be removed and theundercut to effect mating with the base plug flange may then be made.

Preliminary attachment may thereafter be made advantageously by coatingwith resin the mating surfaces of the base plug and gun barrel andrigidly holding the mating surfaces in contact while subjecting them toa curing operation. To promote adherence it is desirable to knurl orroughen the mating surfaces prior to coating with resin.

Final attachment of the base plug to the gun barrel preferably makes useof undercuts on the base plug which promote rigidity and strength ofadherence. These undercuts comprise annular grooves on the periphery ofthe base plug and preferably comprise an annular groove on the lateralperiphery of the end cap and an annular groove on the neck of theknob-shaped projection adjacent the end cap. A continuous layer offiberglass cloth impregnated with resin is wound advantageously warpdirection parallel to longitudinal axis of barrel abut a 6 to 12 inchlongitudinal section of the barrel adjacent the end cap and about theend cap almost to the neck of the knob-shaped projection. The fiberglasscloth is then cut and folded in such a manner as to permit it to liesnugly against the domelike surface of the end cap. The circumferentialfiberglass windings impregnated with resin are thereafter applied overthe fiberglass cloth to compress it around the barrel and end cap anddepress the cloth into the angular groove of the lateral surface of theend cap. Additional circumferential windings are made in the region ofthis angular groove until flush. Repetition of this procedure, with theexception that the windings are carried out helically rather thancircumferentially, and that the windings are carried down to tether theend cap and fill the angular groove at the neck of the projectionadjacent thereto, is continued until about 4 alternate layers of clothand windings are applied. The resultant base plug fitted barrel issubjected to a curing operation wherein it is rotated in an oven at anelevated temperature. Additional circumferential strength may be giventhe adjoining areas by overlaying the last layer of helical windingswith two layers of circumferential windings prior to curing.

The curing cycle comprises about l fliours at about F. and 250 F. andthen about two hours at about 400 F. and 450 F. After this final cure,the mortar gun tube is machined to the desired dimensions and themandrel if, salt, leached out by ordinary tap water, or if made ofaluminum or other material, merely tapped out.

Actual field testing of my monolithic configurated inner liner barrelindicates that over 1,000 81mm. mortar rounds could be firedtherethrough successfully. Slight erosion did occur however at thatportion of the barrel where the hot gases emanate from the mortar flashhole. If my inventive device is employed as the erosion resistant liner,longer barrel vious modifications will occur to a person skilled in theart.

I claim:

1. A tubular device comprising:

a nonstructural inner liner and a structural outer liner, said linersbeing strain-compatible when said tube is subjected to sudden highinternal pressures;

said inner liner being so CO1 lfigurated that inner surfaces of saidouter liner are contacted by said inner liner at uniformly spacedintervals while providing enclosed air spaces at those portions notcontacting said inner surfaces of said outer liner; and

an elastomeric material disposed in said air spaces.

2. The device of claim 1 wherein said inner liner is stainless steel.

3. The device of claim 1 wherein said outer liner is made of fiberglasswrappings.

4. The device of claim 1 wherein said elastomeric material is selectedfrom the group consisting of high temperature silicone, high temperatureepoxy-novolac, high temperature hard resin of high elongation, and hightemperature polyurethane.

5. The device of claim 1 wherein the ratio of outer liner to inner linerthickness is about 20-30 to l.

6. The device of claim 1 wherein said inner liner has a sine waveconfiguration in cross section.

7. The device of claim 1 wherein said inner liner has a square waveconfiguration in cross section.

8. The device of claim 1 wherein said inner liner has a modified squarewave configuration in cross section, as shown in FIG. 3 of the drawings.

9. The device of claim 1 wherein said inner liner has a Z- shapedconfiguration in cross section, as shown in FIG. 4 of the drawing.

10. The device of claim 1 wherein said inner liner has a square waveconfiguration in cross section where uniformly spaced nonadjacent waveshave amplitudes greater than its neighbor, said inner liner beingtwisted relative to its longitudinal axis to provide rifling.

1. A tubular device comprising: a nonstructural inner liner and astructural outer liner, said liners being strain-compatible when saidtube is subjected to sudden high internal pressures; said inner linerbeing so configurated that inner surfaces of said outer liner arecontacted by said inner liner at uniformly spaced intervals whileproviding enclosed air spaces at those portions not contacting saidinner surfaces of said outer liner; and an elastomeric material disposedin said air spaces.
 2. The device of claim 1 wherein said inner liner isstainless steel.
 3. The device of claim 1 wherein said outer liner ismade of fiberglass wrappings.
 4. The device of claim 1 wherein saidelastomeric material is selected from the group consisting of hightemperature silicone, high temperature epoxy-novolac, high temperaturehard resin of high elongation, and high temperature polyurethane.
 5. Thedevice of claim 1 wherein the ratio of outer liner to inner linerthickness is about 20-30 to
 1. 6. The device of claim 1 wherein saidinner liner has a sine wave configuration in cross section.
 7. Thedevice of claim 1 wherein said inner liner has a square waveconfiguration in cross section.
 8. The device of claim 1 wherein saidinner liner has a modified square wave configuration in cross section,as shown in FIG. 3 of the drawings.
 9. The device of claim 1 whereinsaid inner liner has a Z-shaped configuration in cross section, as shownin FIG. 4 of the drawing.
 10. The device of claim 1 wherein said innerliner has a square wave configuration in cross section where uniformlyspaced nonadjacent waves have amplitudes greater than its neighbor, saidinner liner being twisted relative to its longitudinal axis to providerifling.